The present invention relates generally to wireless communications systems and, in particular, to paging a mobile-telephone in a wireless communications system.
The capacity of wireless communications systems is limited by a variety of factors including total transmission power at base stations. FIG. 1 depicts a wireless communication system 10 comprising at least one base station (BS) 12 in communication with a plurality of mobile-telephones (MT) 14-j, where j=1, . . . ,n. BS 12 transmits signals 16-j to MT 14-j over one or more downlink channels. Each signal 16-j has an associated power level Pj at which it is transmitted, wherein the value of power level Pj depends on a variety of factors including distance and interference caused by buildings. The transmission power PBS of BS 12 is equal to the sum of Pj, i.e.,       P    BS    =            ∑              j        =        1                    j        =        n              ⁢          xe2x80x83        ⁢                  P        j            .      
However, PBS cannot exceed a maximum transmission power level Pmax associated with BS 12, i.e., PBSxe2x89xa6Pmax. Thus, the number of mobile-telephones 14-j BS 12 can be in communication simultaneously (i.e., capacity) is limited by Pmax.
Suppose some mobile-telephones in communication with BS 12 are in building 27, see FIG. 2. BS 12 transmits signals 20-k to MT 14-k, wherein each signal 20-k has an associated power level Pk at which it is transmitted, where k=n+1, . . . ,m. In this situation, the transmission power PBS of BS 12 is equal to the sum of Pj and Pk, i.e.,       P    BS    =                    ∑                  j          =          1                          j          =          n                    ⁢              xe2x80x83            ⁢              P        j              +                  ∑                  k          =                      n            +            1                                    k          =          m                    ⁢              xe2x80x83            ⁢                        P          k                .            
However, since mobile-telephones 14-k are indoors, the interference level (due to the presence of building 27) is greater between MT 14-k and BS 12 than between MT 14-j and BS 12. Thus, the power level Pk required for mobile-telephones 14-k to receive signal 20-k at an acceptable signal level will likely be higher than the power level Pj required for mobile-telephones 12-j to receive signal 16-j at an acceptable signal level, i.e., Pk is likely greater than Pj. Because MT 14-k utilize more of BS 12""s transmission power resources, the number of mobile-telephones that BS 12 can be in communication simultaneously is reduced.
One way to increase the capacity in the situation depicted in FIG. 2 is to use a device referred herein as a concentrator. FIG. 2a illustrates a wireless communication system in which a concentrator 25 is incorporated. Concentrator 25 is a device having the functionality of a base station. Specifically, concentrator 25 is configured to communicate with mobile-telephones in building 27, such as MT 14-k, using frequency f2 and with base station 12 using frequency f1. Any transmission from BS 12 to MT 14-k, or vice-versa, goes through concentrator 25. For example, BS 12 transmits a signal having a message intended for MT 14-k to concentrator 25 over a communication channel on frequency f1. Upon receipt of the signal, concentrator 25 demodulates the message and re-modulates the message for re-transmission to MT 14-k over a communication channel on frequency f2, wherein the signal transmitted from BS 12 to concentrator 25 is transmitted at power level Pc. Advantageously, the transmission power Pc associated with a frequency f1 signal being transmitted from concentrator 25 to BS 12 would be less than the transmission power Pk associated with a frequency f1 signal being transmitted from MT 14-k directly to BS 12 (since signal be would not suffer interference due to building 27 before arriving at the concentrator). Thus, the total transmission power PBS of BS 12 would be equal to sum of Pj plus mPc, where m-n-1 corresponds to the number of mobile-telephones inside building 27 in communication with BS 12 via concentrator 25, i.e.,       P    BS    =                    ∑                  j          =          1                          j          =          n                    ⁢              xe2x80x83            ⁢              P        j              +                  (                  m          -          n          -          1                )            ⁢                        P          c                .            
When BS 12 desires to page a mobile-telephone, BS 12 transmits a paging signal using a paging channel on frequency f1 associated with that mobile-telephone. Each mobile-telephones is associated with only one paging channel from a set of paging channels on frequency f1. Thus, different mobile-telephones may be associated with different paging channels on frequency f1. In order for concentrator 25 to detect paging signals on different frequency f1 paging channels intended for MT 14-k in building 27 (and subsequently re-transmit on a paging channel on frequency f2), concentrator 25 needs to be capable of at least monitoring all the paging channels associated with the mobile-telephones 14-k. However, concentrators are typically capable of only monitoring a single paging channel on frequency f1. Thus, unless the paging channel associated with the mobile-telephone to which the paging signal is intended is identical to the paging channel being monitored by (or associated with) concentrator 25, the paging signal will not be detected by concentrator 25 (and will not be re-transmitted to the intended mobile-telephone). According, there exist a need for a concentrator to detect a paging signal intended for a mobile-telephone having an associated paging channel on frequency f1 different than a paging channel on frequency f1 associated with the concentrator.
The present invention is a method and apparatus for detecting a paging signal intended for a mobile-telephone having an associated frequency f1 paging channel different from a frequency f1 paging channel associated with a concentrator. The present invention uses the paging channel on frequency f1 associated with the concentrator to send a paging signal to a mobile-telephone having an associated paging channel on frequency f2 different than the concentrator""s paging channel on frequency f1. In one embodiment, a base station transmits a base station-to-mobile-telephone (BS-MT) paging message by including such BS-MT paging message in a base station-to-concentrator (BS-C) paging message. The BS-MT paging message includes a message portion and a mobile-telephone identifier portion, wherein the mobile-telephone identifier portion indicates the mobile-telephone to which the BS-MT paging message is intended. The BS-C paging message includes the MT paging message and a concentrator identifier portion for indicating the concentrator to which the BS-C is intended. The BS-C paging message is transmitted over a paging channel on frequency f1 associated with the intended concentrator (i.e., concentrator through which the mobile-telephone is linked to the base station). The intended concentrator detects the BS-C paging message by monitoring its associated paging channel on frequency f1 for a BS-C paging message with a concentrator identifier portion indicating the concentrator. Upon detecting its BS-C paging message, the concentrator parses the BS-MT paging message from the BS-C message and transmits the BS-MT paging message to the intended mobile-telephone using a paging channel on frequency f2 being monitored by the mobile-telephone.
In one embodiment, the base station uses a location registry to determine the paging channel on frequency f1 over which to send a BS-MT paging message to the mobile-telephone, wherein the location registry includes information indicating whether a mobile-telephone linked to the base station via a concentrator and, if applicable, a concentrator identifier and an indication of the paging channel associated with the concentrator. If the intended mobile-telephone is linked to the base station via a concentrator, the base station uses the location registry to determine the paging channel on frequency f1 associated with the concentrator before sending a BS-C paging message having the BS-MT paging message on that paging channel.